The present invention relates to apparatus for supplying particulate material to tobacco processing and analogous machines. For example, the apparatus of the present invention can be utilized to supply fragments of tobacco leaves to the distributor of a cigarette rod making machine. The term "particulate material" is intended to embrace all kinds of particulate materials which can be transported in a gaseous carrier medium, and such material includes shredded tobacco, otherwise fragmentized tobacco leaves, fragments of tobacco ribs, fragments of reconstituted tobacco as well as all kinds of smokable tobacco substitute materials.
It is well known to supply shredded or otherwise comminuted tobacco from a source of supply to the magazine of the distributor of a cigarette rod making machine by resorting to a pneumatic conveyor which draws particles of tobacco from the source and contains a suitable segregating device which separates the entrained solid particulate material from the gaseous carrier medium. It is desirable to operate the supplying apparatus in such a way that the magazine of the processing machine, such as the aforementioned cigarette rod making machine, invariably contains a substantially constant supply of particulate material. It is further preferred to supply relatively small quantities of particulate material at a relatively high frequency rather than resorting to admission of large batches of particles at less frequent intervals because the level of the supply of particulate material in the magazine is more constant if the material is admitted more or less continuously and in such a way that the quantity of stored material on admission of a batch does not undergo a pronounced change. It has been discovered that a cigarette rod making machine is much more likely to produce a relatively thin and homogeneous layer of tobacco particles, which can be readily converted into a rod-like filler of constant density and diameter, if the particles of tobacco are drawn from a magazine wherein the level of the supply of tobacco particles is constant or fluctuates within a narrow range. Measurements indicate that the weight of rod-shaped smokers' products is much more uniform if the magazine in the distributor of the cigarette rod making machine contains a substantially constant supply of tobacco particles.
A modern cigarette rod making machine can turn out many thousands of plain cigarettes per minute. Consequently, the pneumatic conveyor which delivers comminuted tobacco to the magazine of the distributor of such machine must convey the particles of tobacco at a very high rate. However, the output of a pneumatic conveyor cannot be increased at will because particles of tobacco are likely to be damaged if the speed of the gaseous carrier medium exceeds a certain maximum acceptable value. For example, pneumatic transport at an excessive speed can entail comminution of larger particles so that the product contains an excessive percentage of shorts and dust. Moreover, if the speed of the gaseous carrier medium is increased above a certain value, the carrier medium is likely to effect a highly undesirable classification of conveyed particles, namely segregation of comminuted tobacco ribs from shredded tobacco leaf laminae. Such classification is undesirable because it reduces the homogeneousness of the tobacco filler which is draped into a web of cigarette paper to form a cigarette rod ready to be subdivided into plain cigarettes of unit length or multiple unit length. Still further, if the gaseous carrier medium is caused to flow at an excessive speed, particles of dust and short tobacco, which should not enter the magazine of the distributor in a cigarette rod making machine, cannot be readily separated from the heavier and larger (satisfactory) tobacco particles so that the segregating action is less than satisfactory as soon as the speed of the carrier medium exceeds the aforementioned maximum permissible value. It should be borne in mind that one of the important reasons for entraining tobacco particles from the source to the consumer by pneumatic means is the possibility of simultaneously and reliably segregating dust and shorts from more acceptable particulate material.